1. Field of the Invention
The present invention is related to a rolling bearing having high sealing performance and also to a throttle valve apparatus and an anti-lock brake system (hereinafter referred to as the “ABS”) which include the rolling bearing.
2. Description of the Related Art
For example, in a throttle valve apparatus of an internal combustion engine, a structure where both ends of a throttle shaft rotatably driving a butterfly valve which opens/closes an air intake passage are supported by rolling bearings is well known. The rolling bearing for such structure requires good sealing performance (air tightness) for preventing intake-air leakage. Further, the rolling bearing is configured to receive the intake negative pressure of an engine and also to receive supercharging pressure in the case of an engine with a supercharger. Since these pressures fluctuate greatly depending on the operating condition of the engine, the rolling bearing needs to maintain sufficient air-tightness against these large pressure fluctuations.
In contrast, Japanese Patent Application Laid-Open (JP-A) No. 2004-263734 (hereinafter referred to as Reference 1) discloses a seal structure in which the annular space between the inner ring and the outer ring is sealed by a pair of annular seal members provided on both ends of the rolling bearing (especially refer to FIG. 6 of Reference 1). In the above seal structure, however, if a pressure higher than the atmospheric pressure is applied to one of the pair of seal members from the outside, a lip part of the seal member may be rolled up to the side of the annular space. As a result, the internal pressure of the annular space may increase, and the other seal member may be rolled up to the outside and may separate from the rolling bearing.
Further, Reference 1 also discloses a rolling bearing which is configured in that, even when a pressure higher than the atmospheric pressure is applied from the outside to one of the seal members and the lip part thereof is moved toward the annular space side, the movement of the lip part may be limited by a step portion provided on an outer peripheral surface of the inner ring (especially refer to FIG. 1 of Reference 1). In the above rolling bearing, however, since the step portion, i.e. the portion contacted by the lip part, is usually finished by cutting process, it results in an inferior surface accuracy compared to the surface accuracy finished by grinding process. Therefore, it is difficult to obtain a high sealing performance at the step portion.
In addition, grinding the step portion may increase the manufacturing cost because a low cost centerless grinding process cannot be performed to the step portion.